Skin conditions momentarily change with variable factors such as a seasonal factor and physical conditions, and also change as a result of skin care taken by applying cosmetics or the like. Accordingly, it is an important factor to appropriately select cosmetics in accordance with the change for the purposes of antiaging and maintaining the skin beautiful in its appearance. For this reason, there have been devised various methods of objectively and scientifically differentiating skin appearances and conditions thereof. An example of those methods includes a method in which corneocytes are collected from the facial skin of a subject by an adhesive tape or an adhesive disk, the corneocytes are stained, and the skin condition is differentiated by using a microscope or the like based on criteria such as the regularity in the alignment of the corneocytes, the shape of the corneocytes, the area of the corneocytes, the degree of exfoliation of the corneocytes, and the presence or absence of a nucleus in the corneocytes.
As for the technology as described above, there have been disclosed methods described below. According to one of the methods, corneocytes are stained brilliant green and gentian violet to differentiate the shape of the corneocytes, based on which the skin condition is estimated, to thereby allow appropriate selection of cosmetics (see, for example, Patent Document 1). Another method includes a dyeing method capable of determining with accuracy the area and the shape of skin corneocytes by using a tannic acid or the like as a mordant (see, for example, Patent Document 2). There has been disclosed further another method capable of easily dyeing corneocytes instantaneously and uniformly by using a liquid dye for corneocytes, the liquid dye containing, equal to or lower than 50% by mass of an alcohol content having from 1 to 4 carbon atoms, a dye, an aromatic alcohol, and an organic acid (see, for example, Patent Documents 3 and 4).
According to the conventional differentiation methods as described above, however, it has often been difficult to secure time required for the dyeing, contamination in the area around the dyeing workplace, or to secure the dyeing workplace itself.
Accordingly, it has been an important issue to develop a skin differentiation method which does not require the dyeing work at all.
However, in reality, the differentiation method as described above which does not require at all the work of dyeing corneocytes has not been realized so far.
Meanwhile, there is a great amount of accumulated analytical data which has been obtained by using stained specimens of corneocytes. Therefore, it is desired for an unstained specimen of corneocytes to allow an easy comparison with the above-mentioned past data.
At the same time, in the field of displays such as television, along with the rapid proliferation of such technologies as a color liquid crystal display technology and a plasma display technology, there has been disclosed a color adjusting method in which fine tones of color, such as shading in an observation target to be displayed as an image, is adjusted and displayed in pseudocolor, to thereby facilitate observation and visual operation (see, for example, Patent Documents 5, 6, and 7). However, no attempt has been implemented at all, by experts in image processing and experts in skin differentiation, to apply the idea in the color adjusting method employed in the above-mentioned image processing to the differentiation of unstained corneocytes, and there has not been found any document indicating the application.    Patent Document 1: Japanese Patent Application Laid-open No. 2003-203336    Patent Document 2: Japanese Patent Application Laid-open No. 2000-125854    Patent Document 3: Japanese Patent Application No. 2004-266335    Patent Document 4: Japanese Patent Application No. 2005-257451    Patent Document 5: Japanese Patent Application Laid-open No. Hei 08-163387    Patent Document 6: Japanese Patent Application Laid-open No. Hei 05-183739    Patent Document 7: Japanese Patent Application Laid-open No. Hei 11-98372